Fresh Air Door; Checking Approximate Airflow - Friedrich VERT-I-PAK VHA09K25RTQ Service Manual

Fresh Air Door

The Fresh Air Door is an "intake" system. The fresh air door opened via a slide on the front of the chassis located just above the indoor
coil. Move the slide left to open and right to close the fresh air door. The system is capable of up to 60 CFM of fresh air @ ~.3" H2O
internal static pressure.

Checking Approximate Airflow

If a digital manometer is not available to check the External Static Pressure, or the blower performance data is unavailable for your unit,
Kilowatts × 3413
approximate airflow can be calculated by measuring the temperature rise, then using tile following criteria.
CFM =
Temp Rise × 1.08
Electric Heat Strips
The approximate CFM actually being delivered can be calculated by using the following formula:
DO NOT simply use the Kilowatt Rating of the heater (i.e. 2.5, 3.4, 5.0) as this will result in a less-than-correct airflow calculation. Kilowatts
may be calculated by multiplying the measured voltage to the unit (heater) times the measured current draw of all heaters (ONLY) in
operation to obtain watts. Kilowatts are than obtained by dividing by 1000.
EXAMPLE: Measured voltage to unit (heaters) is 230 volts. Measured Current Draw of strip heaters is 11.0 amps.
230 x 11.0 = 2530
2530/1000 = 2.53 Kilowatts
2.53 x 3413 = 8635
Supply Air = 95°F
Return Air = 75°F
Temperature Rise = 20°F
8635
20 x 1.08 = 21.6
= 400
21.6
30
External Static Pressure